1. Field of the Disclosure
Embodiments of the present invention relate to a display device, and more particularly, to a display device with an integrated in-cell type touch screen.
2. Discussion of the Related Art
Touch screens are a type of input device that may be included in display devices such as Liquid Crystal Displays (LCDs), Field Emission Displays (FEDs), Plasma Display Panel (PDPs), Electroluminescent Displays (ELDs), and Electrophoretic Display (EPDs), and may enable a user to input information by directly touching a screen with a finger, a pen or the like while looking at the screen of the display device.
Particularly, the demand of display devices with an integrated in-cell type touch screen, which may include a plurality of built-in elements configuring the touch screen, is recently increasing. Such display devices may be used in slim-profile portable terminals such as smart phones and tablet Personal Computers (PCs).
In a related art display device with an integrated in-cell type touch screen disclosed in U.S. Pat. No. 7,859,521, a plurality of common electrodes for a display are segmented into a plurality of touch driving areas and touch sensing areas, thereby allowing a mutual capacitance to be generated between the touch driving area and the touch sensing area. Therefore, the related art display device measures the change of a mutual capacitance that occurs from a touch, and thus determines whether there is a touch.
In other words, in the related art display device with an integrated in-cell type touch screen, a plurality of common electrodes for the display perform the function of a touch electrode when a panel operates in a touch driving mode. This allows the display device to simultaneously perform a display function and a touch function.
In a related art in-cell type mutual capacitive touch screen using the existing common electrodes, a scheme that uses a plurality of driving electrodes and sensing electrodes necessary for touch driving temporally separates a display driving mode session and a touch driving mode session by using a common electrode, and thus prevents a noise ingredient (which occurs in the display driving mode session) from affecting the touch driving.
In the display driving mode session, a driving electrode and a sensing electrode act as common electrodes. In the touch driving mode session, a periodic driving pulse is applied to a driving electrode, and a touch integrated circuit (IC) determines whether there is a touch by using a touch sensing signal that is generated between a sensing electrode and the driving electrode according to the driving pulse applied to the driving electrode.
Specifically, a ground voltage applied to the touch IC is used as the low-level voltage of the driving pulse applied to the driving electrode. Also, an arbitrary direct current (DC) voltage instead of a ground voltage is applied to a receiver of the touch IC connected to a sensing electrode for detecting the signal of the sensing electrode.
FIG. 1 is a timing chart showing voltages which may be respectively applied to a driving electrode and sensing electrode of a related art display device with an integrated touch screen.
For example, as shown in FIG. 1, in a display driving mode session, a common voltage Z(V) may be applied to both the driving electrode TX and the sensing electrode RX, and thus, an equal voltage may be generated between the driving electrode and the sensing electrode, whereby an image-quality defect such as block dimming caused due to a luminance difference between the electrodes may be avoided.
However, in a touch driving mode session, a driving pulse where X(V) may be a high-level voltage and a ground voltage may be a low-level voltage may be applied to the driving electrode TX, and a touch sensing reference voltage Y(V) that may be a constant DC voltage may be applied to a receiver of a touch IC connected to the sensing electrode RX.
Here, as shown in FIG. 1, the driving pulse may be applied to the driving electrode in only part of a session, and the ground voltage that may be the low-level voltage may be applied to the driving electrode in most of a session.
Therefore, a difference between voltages respectively applied to the driving electrode and the sensing electrode may occur in the touch driving mode session, and thus, different voltages may be applied to a common electrode block that is used as a driving electrode and a common electrode block that is used as a sensing electrode in the touch driving mode session. This may cause block dimming in which a luminance difference occurs between blocks in a panel.
Moreover, as shown in FIG. 1, the common voltage Z(V) may be applied to the driving electrode and the sensing electrode in the display driving mode session, but in the touch driving mode session, the ground voltage (which may have a level different from that of the common voltage) may be applied to the driving electrode, and the touch sensing reference voltage Y(V) may be applied to the sensing electrode, thereby causing flickers due to a voltage difference between the display driving mode session and the touch driving mode session.